pg_sema.h File Reference

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Typedefs
typedef struct PGSemaphoreData *	PGSemaphore

Functions
void	PGSemaphoreShmemRequest (int maxSemas)
void	PGSemaphoreInit (int maxSemas)
PGSemaphore	PGSemaphoreCreate (void)
void	PGSemaphoreReset (PGSemaphore sema)
void	PGSemaphoreLock (PGSemaphore sema)
void	PGSemaphoreUnlock (PGSemaphore sema)
bool	PGSemaphoreTryLock (PGSemaphore sema)

Typedef Documentation

PGSemaphore

typedef struct PGSemaphoreData* PGSemaphore

Definition at line 34 of file pg_sema.h.

Function Documentation

PGSemaphoreCreate()

PGSemaphore PGSemaphoreCreate ( void  )

extern

Definition at line 255 of file posix_sema.c.

{
    PGSemaphore sema;
    sem_t      *newsem;
 
    /* Can't do this in a backend, because static state is postmaster's */
    Assert(!IsUnderPostmaster);
 
    if (numSems >= maxSems)
        elog(PANIC, "too many semaphores created");
 
#ifdef USE_NAMED_POSIX_SEMAPHORES
    newsem = PosixSemaphoreCreate();
    /* Remember new sema for ReleaseSemaphores */
    mySemPointers[numSems] = newsem;
    sema = (PGSemaphore) newsem;
#else
    sema = &sharedSemas[numSems];
    newsem = PG_SEM_REF(sema);
    PosixSemaphoreCreate(newsem);
#endif
 
    numSems++;
 
    return sema;
}

References Assert, elog, ereport, errmsg, fb(), IpcSemaphoreCreate(), IpcSemaphoreInitialize(), IsUnderPostmaster, maxSemaSets, maxSems, maxSems, maxSharedSemas, mySemaSets, mySemSet, nextSemaNumber, numSemaSets, numSems, numSems, numSharedSemas, PANIC, PG_SEM_REF, PosixSemaphoreCreate(), SEMAS_PER_SET, PGSemaphoreData::semId, PGSemaphoreData::semNum, sharedSemas, and sharedSemas.

Referenced by ProcGlobalShmemInit().

PGSemaphoreInit()

void PGSemaphoreInit ( int  maxSemas )

extern

Definition at line 198 of file posix_sema.c.

{
    struct stat statbuf;
 
    /*
     * We use the data directory's inode number to seed the search for free
     * semaphore keys.  This minimizes the odds of collision with other
     * postmasters, while maximizing the odds that we will detect and clean up
     * semaphores left over from a crashed postmaster in our own directory.
     */
    if (stat(DataDir, &statbuf) < 0)
        ereport(FATAL,
                (errcode_for_file_access(),
                 errmsg("could not stat data directory \"%s\": %m",
                        DataDir)));
 
#ifdef USE_NAMED_POSIX_SEMAPHORES
    mySemPointers = (sem_t **) malloc(maxSemas * sizeof(sem_t *));
    if (mySemPointers == NULL)
        elog(PANIC, "out of memory");
#endif
 
    numSems = 0;
    maxSems = maxSemas;
    nextSemKey = statbuf.st_ino;
 
    on_shmem_exit(ReleaseSemaphores, 0);
}

References DataDir, elog, ereport, errcode_for_file_access(), errmsg, FATAL, fb(), malloc, maxSemaSets, maxSems, maxSems, maxSharedSemas, mySemaSets, mySemSet, nextSemaKey, nextSemaNumber, nextSemKey, numSemaSets, numSems, numSems, numSharedSemas, on_shmem_exit(), PANIC, ReleaseSemaphores(), ReleaseSemaphores(), ReleaseSemaphores(), SEMAS_PER_SET, and stat.

Referenced by ProcGlobalShmemInit().

PGSemaphoreLock()

void PGSemaphoreLock ( PGSemaphore  sema )

extern

Definition at line 313 of file posix_sema.c.

{
    int         errStatus;
 
    /* See notes in sysv_sema.c's implementation of PGSemaphoreLock. */
    do
    {
        errStatus = sem_wait(PG_SEM_REF(sema));
    } while (errStatus < 0 && errno == EINTR);
 
    if (errStatus < 0)
        elog(FATAL, "sem_wait failed: %m");
}

References CHECK_FOR_INTERRUPTS, EINTR, elog, ereport, errmsg, FATAL, fb(), PG_SEM_REF, pgwin32_dispatch_queued_signals(), pgwin32_signal_event, PGSemaphoreData::semId, and PGSemaphoreData::semNum.

Referenced by BufferLockAcquire(), BufferLockDequeueSelf(), LWLockAcquire(), LWLockAcquireOrWait(), LWLockDequeueSelf(), LWLockWaitForVar(), ProcArrayGroupClearXid(), and TransactionGroupUpdateXidStatus().

PGSemaphoreReset()

void PGSemaphoreReset ( PGSemaphore  sema )

extern

Definition at line 288 of file posix_sema.c.

{
    /*
     * There's no direct API for this in POSIX, so we have to ratchet the
     * semaphore down to 0 with repeated trywait's.
     */
    for (;;)
    {
        if (sem_trywait(PG_SEM_REF(sema)) < 0)
        {
            if (errno == EAGAIN || errno == EDEADLK)
                break;          /* got it down to 0 */
            if (errno == EINTR)
                continue;       /* can this happen? */
            elog(FATAL, "sem_trywait failed: %m");
        }
    }
}

References EAGAIN, EINTR, elog, FATAL, fb(), IpcSemaphoreInitialize(), PG_SEM_REF, PGSemaphoreTryLock(), PGSemaphoreData::semId, and PGSemaphoreData::semNum.

Referenced by InitAuxiliaryProcess(), and InitProcess().

PGSemaphoreShmemRequest()

void PGSemaphoreShmemRequest ( int  maxSemas )

extern

Definition at line 165 of file posix_sema.c.

{
#ifdef USE_NAMED_POSIX_SEMAPHORES
    /* No shared memory needed in this case */
#else
    /* Need a PGSemaphoreData per semaphore */
    ShmemRequestStruct(.name = "Semaphores",
                       .size = mul_size(maxSemas, sizeof(PGSemaphoreData)),
                       .ptr = (void **) &sharedSemas,
        );
#endif
}

References fb(), mul_size(), name, sharedSemas, sharedSemas, and ShmemRequestStruct.

Referenced by ProcGlobalShmemRequest().

PGSemaphoreTryLock()

bool PGSemaphoreTryLock ( PGSemaphore  sema )

extern

Definition at line 358 of file posix_sema.c.

{
    int         errStatus;
 
    /*
     * Note: if errStatus is -1 and errno == EINTR then it means we returned
     * from the operation prematurely because we were sent a signal.  So we
     * try and lock the semaphore again.
     */
    do
    {
        errStatus = sem_trywait(PG_SEM_REF(sema));
    } while (errStatus < 0 && errno == EINTR);
 
    if (errStatus < 0)
    {
        if (errno == EAGAIN || errno == EDEADLK)
            return false;       /* failed to lock it */
        /* Otherwise we got trouble */
        elog(FATAL, "sem_trywait failed: %m");
    }
 
    return true;
}

References EAGAIN, EINTR, elog, ereport, errmsg, EWOULDBLOCK, FATAL, fb(), IPC_NOWAIT, PG_SEM_REF, PGSemaphoreData::semId, and PGSemaphoreData::semNum.

Referenced by PGSemaphoreReset().

PGSemaphoreUnlock()

void PGSemaphoreUnlock ( PGSemaphore  sema )

extern

Definition at line 333 of file posix_sema.c.

{
    int         errStatus;
 
    /*
     * Note: if errStatus is -1 and errno == EINTR then it means we returned
     * from the operation prematurely because we were sent a signal.  So we
     * try and unlock the semaphore again. Not clear this can really happen,
     * but might as well cope.
     */
    do
    {
        errStatus = sem_post(PG_SEM_REF(sema));
    } while (errStatus < 0 && errno == EINTR);
 
    if (errStatus < 0)
        elog(FATAL, "sem_post failed: %m");
}

References EINTR, elog, ereport, errmsg, FATAL, fb(), PG_SEM_REF, PGSemaphoreData::semId, and PGSemaphoreData::semNum.

Referenced by BufferLockAcquire(), BufferLockDequeueSelf(), BufferLockWakeup(), IpcSemaphoreCreate(), LWLockAcquire(), LWLockAcquireOrWait(), LWLockDequeueSelf(), LWLockUpdateVar(), LWLockWaitForVar(), LWLockWakeup(), ProcArrayGroupClearXid(), and TransactionGroupUpdateXidStatus().